Vacuum flushing of an injector for internal combustion engines

ABSTRACT

A method for flashing air from an injection valve such as a common rail injector for an internal combustion engine which injection valve on being put into operation is initially at least partly filled with air and to which a liquid medium is supplied via a typical connection for supplying fuel, including pressurizing an inner chamber of the injection valve to a pressure that is reduced compared to normal operation, whereby existing air bubbles increase in volume compared to the volume in normal operation, and flushing the medium contained in the aforementioned inner chamber at a reduced pressure that remains at least approximately constant, and selectively repeating these steps multiple times. The operational readiness of the injector, despite air in the gas phase that is initially contained inside it in the liquid medium, can be brought about rapidly as a result. An apparatus for performing the method is also disclosed.

The invention relates to a method as defined by the preamble to claim 1.The invention is particularly important in common rail injectors. Aninjector of this kind, which does not itself cause any pressure increasebut instead is supplied directly with the fuel under pressure forinjection into the engine, in particular a diesel engine, reactssensitively to air components in the medium processed by the injector.This medium in the case of an operationally ready diesel engine isdiesel fuel, but in the testing field, the testing medium in measurementand testing of the injector is typically not diesel fuel but rather ahydraulically similar material that is preferably noncombustible. Airinclusions in the injector, which are present when the injector isfilled with the medium before it is put into operation, must be flushedout to a low-pressure connection (leakage connection) of the injectorvia the volumetric flow of the return quantity of the medium thatresults during normal operation, for instance from leak fuel quantitiesand/or from the actuation of a control valve.

The air, present in the gas phase, has much greater compressibility thanthe liquid medium, and as a result the dynamic damping behavior in theinjector, in particular in a magnet valve, is influenced in anonreplicable way and has a direct effect on the injection quantity.This makes measurements more difficult in the testing field. In the caseof a vehicle that has a diesel engine and is ready for operation and inwhich an injector has for instance just been replaced in the repairfacility and is filled for the first time with diesel fuel, the existinggaseous air once again causes nonreplicable injection events, which fora brief time can make driving feel uncomfortable and make it impossibleto meet the required values for exhaust gas. Dissolved air contained inthe medium is not considered problematic in this particular application,as long as the air remains dissolved during the entire operating stateof the injector and does not become gaseous.

The magnet valve mentioned may in particular be a control valve, whichvia an outflow throttle enables the outflow of medium from a controlchamber of a stroke-controlled injector in order to bring about aninjection event, and which blocks to end the injection event. Variousmoving and nonmoving parts of the magnet valve (for instance, see FIG.2: armature, at least one spring, closure element to be actuated forenabling the outflow; nonmoving guide of the armature) are disposed in afunction chamber. This function chamber and the parts of the controlvalve that are contained in it have numerous edges and protrusions,which have a tendency to trap air bubbles, if the air bubbles do notexceed a certain size, so that in normal operation it can takeconsiderable time (from many seconds to approximately 1 minute) untilthis function chamber contains only so little air in the gaseous statethat practically no disruption of the function of the internalcombustion engine, for instance in measurement, occurs.

The function chamber generally communicates directly with a low-pressureconnection, that is, without the interposition of special blockingdevices. In operation of the injector at ambient pressure, which for thesake of simplicity is considered to be 1 bar (absolute) or 0 bar(relative), in internal combustion engines at least a slightoverpressure (such as 0.5 bar) relative to the ambient pressure is oftenmaintained at the low-pressure connection, to prevent leak fuel linesfrom running empty. Combustion power plants exist in which aconsiderably greater pressure prevails in operation at the low-pressureconnection of the injector (for instance, 10 bar), such as in injectorswhose control valve is actuated by a piezoelectric actuator, preferablyvia a hydraulic coupler. Even in this kind of injector, it may beadvantageous to make it air-free with the invention.

The object of the invention is to bring about the operational readinessof the injector rapidly, despite gaseous air contained inside it in theliquid medium, or in other words in the case of a pneumatic/hydraulicfilling of the injector.

ADVANTAGES OF THE INVENTION

The characteristics of the method of the invention as described in claim1 have the effect that the gaseous air, because of the pressure drop,forms such large air bubbles that they cannot stay caught on protrusionsof any kind in the injector. As a result, the air is maximally removed,and an unambiguously replicable fill state of the injector in testing inthe testing field or in operation in a motor vehicle is quickly reached.

The pressure drop should not be so great that the vapor pressure of theliquid medium, or of parts of it, is reached or undershot. The rapidelimination of the return quantity enriched with gas bubbles can bespeeded up by flushing them away with an air-free medium, at aconsiderably lower pressure than the common rail pressure. In the caseof the motor vehicle, this medium may be fuel originating directly fromthe fuel tank.

The apparatus of the invention as defined by claim 4 has devices forconnecting an injector to a source of high pressure of the medium and toa underpressure connection. A control device with control terminals ofswitching valves is advantageous and is also advantageously coupled to atrigger circuit for opening and closing the injection openings of theinjector.

DRAWING

A preferred embodiment of an arrangement with which one type ofembodiment of a method of the invention can be realized is shownschematically in the drawing and will be described in further detail inthe ensuing description. Shown are:

FIG. 1, a hydraulic basic circuit diagram of the arrangement foreliminating air inclusions from a common rail injector, an arrangementthat is used both in the testing field, the first time the injectionsystem is put into operation at the automobile manufacturer, or may alsobe present in a well-equipped automotive repair facility,

FIG. 2, a longitudinal section through a known stroke-controlledinjector for diesel fuel, having a magnet valve, which via an outflowthrottle controls the pressure in a control chamber for the sake ofactuating a valve piston for opening and closing injection openings; and

FIG. 3, a timing diagram of the triggering of the valves V1 through V4.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The arrangement 1 shown in FIG. 1 schematically shows an injector 2,installed in the arrangement, for common rail operation, having ahigh-pressure connection 3 for the liquid test medium, which is free ofgaseous air. This medium can be supplied from a connection 5, at whichthe test medium is available at high pressure, via a pipeline 6. In thetest field, the injector 2 has been inserted into the completely emptystate, that is, filled only with air, into the arrangement 1 is shown,or with a mixed filling (air and a test medium), for instance in thecase of repeated tests.

In the example, the injector has a connection 7 for electricallytriggering a magnetic control valve 8, which upon triggering reduces thepressure in a control chamber 10 (FIG. 2) via an outflow throttle 9 inorder to control the opening of injection openings 11 by means of avalve piston 12.

Leak fuel quantities, which depending on the embodiment of the injectoralso a relatively large return quantity that occurs during operation,from the injector flow away from the injector via a connection 13(low-pressure connection, leakage connection). In this example, thisconnection is not connected directly to a pipeline, serving for instanceas a return line into the fuel tank, but instead to an adaptor head 14,which makes it possible to connect the connection 13 to otherconnections of the arrangement.

This includes a vacuum pump 16, which via a pipeline 17 and a pipebranch 18 is in communication with a pipeline 19 communicating with theadaptor head; it also includes a tank 20 for receiving theaforementioned return quantity, which tank is in communication with thepipe branch 18 via a pipeline 21. A low-pressure connection 22 for alow-pressure medium, in this case called a flushing medium, is alsoprovided; via a pipeline 24 and a throttle 25, it is supplied to aconnection, diametrically opposite the pipeline 19, of the adaptor head14. As a result, the flushing medium can flush air bubbles 30, whichreach the adaptor head 14 from the injector 2, out in the directiontoward the left in the drawing. The function of the entire arrangementis controlled by switching valves, specifically one switching valve V1in the line 17, one switching valve V2 in the line 24, one switchingvalve V3 in the line 21, and one switching valve V4 in the line 6.Electrical control terminals of the switching valves are connected to acontrol device that controls the sequence of the method.

The function sequence will now be explained in terms of the curvecourses shown in FIG. 3, which with their bottom line indicate theclosed state of the associated switching valve and with their lineextending above the bottom line indicate the opened state of thatswitching valve.

Initially, all the switching valves V1 through V4 are blocked. Theswitching valves V1 and V4 are then opened; that is, underpressure isapplied to the arrangement, and simultaneously, medium at the highpressure (for instance, 1600 bar for a typical injector) is supplied tothe connection 3 of the injector 2.

The underpressure generated by the vacuum pump 16 acts on the connection13 of the injector via the adaptor head 14 and also on the hydraulicinternal volume of the injector, as long as the injector is incommunication with the connection 13, and in particular acts on thechamber in which the control valve is located. Simultaneously, via thepipelines 17 and 19, the adaptor head 14, and the connection 13, thevacuum aspirates test medium out of the injector; initially, the firsttime, there may possibly still be a very great deal of air that is notin the form of bubbles. Any air bubbles originally present haveincreased in size relative to their original state because of the vacuum(if the pressure is reduced from 1 bar to 0.1 bar, for instance, theywill have approximately doubled in diameter) and now can no longer catchso easily on any protrusions and are therefore flushed out by theconstantly produced return quantity from the injector.

Via a trigger circuit 7′, coupled to the aforementioned control device,a trigger signal is supplied to the electrical terminal 7 and triggersthe injector, in this example, in the usual way for operation of aninternal combustion engine; in this example, it does so with 1000electrical pulses per minute, so that per minute, the control valve 8executes 1000 opening and closing events. (This is very much faster thanthe switching frequency of the control valve 2, for instance.) Duringthat time, leakage fluid and control fluid, which occurs in the strokeof the valve piston 12, flows out through the connection 13 and, becauseof the existing underpressure in the region of the control valve,flushes out air bubbles, which are enlarged compared to normaloperation. The flushed-out air bubbles reach the adaptor head 14, wherein a preferred embodiment of the method they are flushed out of theadaptor head by flushing medium, which is released by the valve V2 atotal of three times in the example shown, and as a result theelimination of air from the vicinity of the injector is reinforced.

For the sake of simple handling of the system, the vacuum pump 16 isembodied such that it aspirates not only air but also any medium or fuelthat occurs. In other embodiments of the method and the apparatus, thevacuum pump 16 aspirates only air; the mixture of air bubbles and liquidmedium flowing vertically upward through the line 17 in this examplepasses from above, still under a vacuum, into a collection tank, wherethe liquid medium accumulates, and the vacuum pump is connected abovethe collection tank and thus does not come into contact with the liquidmedium. The aforementioned collection tank must be emptied from time totime.

Once the aforementioned arrangement 1 as just described has been inoperation for a few seconds, for instance, the switching valve V1(vacuum) will have been closed in the meantime. In this example, this isfollowed by a single flushing operation as well. The high-pressuresupply of test medium via the switching valve V4 is maintained, and theswitching valve V3 is opened, so that the now sufficiently air-freemedium continuing to emerge from the low-pressure connection 13 of theinjector 2 is delivered, given further delivery of the medium to thehigh-pressure connection 3, through the valve V4 to the collection tank20, as is provided in normal operation in the motor vehicle, and can bemeasured (quantified) as needed.

Following the time sequence of the activity of the valves describedhere, a measurement of the properties of the injector may now be made inthe test field, or in the case of a combustion injection valve freshlyinserted into an internal combustion engine, this injection valve isair-free, and the arrangement used for making it air-free can be removedfrom the engine after the engine is shut off, and then standardconnections of the engine, which must be undone in order to attach themeasuring equipment, are restored again.

In FIG. 1, measuring instruments or points, symbolized by pointerinstruments, for the vacuum, the low-pressure flushing medium and thehigh-pressure test medium are provided, by which the activity of thesystem can be monitored and its measurement values can be recorded in alog.

At the times t1 through t6 shown in FIG. 3, of which t1 is shortlybefore the opening of the valves V1 and V4 and t6 is shortly after theclosure of V1, but the valve V2 is still open (carrying liquid), and theother times are each associated with open and blocked states of thevalve V2, the following absolute pressures prevail in the region of thelow-pressure connection 13 of the injector 2, along with the associatedrelative sizes of the individual air bubbles in the region of thecontrol valve 8, expressed in the form of volumes:

-   t1: absolute pressure 0.1 bar, air bubble volume 10;-   t2: absolute pressure 2.6 bar, air bubble volume 0.38;-   t3: absolute pressure 0.1 bar, air bubble volume 10;-   t4: absolute pressure 2.6 bar, air bubble volume 0.38;-   t5: absolute pressure 0.1 bar, air bubble volume 10;-   t6: absolute pressure 4 bar, air bubble volume 0.25.

FIG. 3 must be understood solely as an illustration; in practice, moreflushing operations (or not even a single flushing operation) andmultiple repetitions of the operation shown may be performed.

In the performance of the method of the invention and in the activity ofthe apparatus of the invention, the number and in particular the totalvolume of the air bubbles present in the injector decreases steadily,because new, air-free medium is constantly being supplied to theconnection 3, and after a short time, at most after only a few seconds,the injector is practically air-free, and measurements can now be madeexactly at the injector.

If the described apparatus 1 is to be used for instance in aprofessional automotive facility for instance to install a repaired andstill air-filled injector in an internal combustion engine, then allthat is needed is to connect the above-described system parts to theinjector, that is, the adaptor head, and with it the vacuum pump. Thesupply of high-pressure medium, in this case specifically diesel fuel,already exists in the motor vehicle, without special provisions beingrequired. It may be that in this case difficulties arise in furnishing alow-pressure flushing medium, namely once again specifically dieselfuel. In that case, the adaptor head for use in the professionalfacility would not have a connection for flushing medium, or thatconnection would be closed.

It may be practical to free still other injectors, such as injectors ofthe kind those that put fuel of relatively low pressure at the injectionpressure via a built-in compressor, of air inclusions by using theinvention.

It is assumed that the influence of air bubbles in a magnet valve, ashas just been explained, is especially troublesome, because for instancea delay in the opening motion of the armature of the magnet valve, or afaster opening motion as a consequence of air inclusions, compared tothe desired state, leads to a delayed or accelerated increase in themagnetic force acting on the armature, making the influence on thefunction of the magnet valve especially strong.

The invention can also be usefully applied to other types of controlvalves, in particular in the case of a control valve that is actuatedvia a piezoelectric actuator, even if this actuator, because of theabsence of the just-described joint coupling effect in the case of anelectromagnetic valve might possibly be less strongly affected in itsfunction by the presence of air bubbles. In both types of valvesmentioned, it may be especially troublesome that once a largelyair-filled injection valve is put into operation, the development offoam can initially occur in the region where the moving parts of thecontrol valve are located, making measurement more difficult or evenimpossible. Such injectors, which if a hydraulic coupler is presentrequire a counterholding pressure at the leakage connection of 10 bar,for instance, in normal operation, can be freed of air inclusions in theway described here and in the process normally be exposed to theaforementioned low pressure of 0.1 bar, which not applied for very long.

1-9. (canceled)
 10. A method for flushing air from injection valve suchas a common rail injector for an internal combustion engine whichinjection valve on being put into operation is initially at least partlyfilled with air and to which a liquid medium is supplied via a typicalconnection for supplying fuel, the method comprising pressurizing aninner chamber of the injection valve to a pressure that is reducedcompared to normal operation, whereby existing air bubbles increase involume compared to the volume in normal operation, and flushing themedium contained in said inner chamber, at a reduced pressure thatremains at least approximately constant, and selectively repeating thesesteps multiple times.
 11. The method according to claim 10, furthercomprising supplying control signals for opening and closing theinjection to the injection valve.
 12. The method according to claim 10,further comprising supplying a low-pressure medium to reinforce theflushing out of the medium after leaving the injection valve.
 13. Themethod according to claim 11, further comprising supplying alow-pressure medium to reinforce the flushing out of the medium afterleaving the injection valve.
 14. An apparatus for performing the methodaccording to claim 10, the apparatus comprising: an adaptor head (14),to be connected to a low-pressure connection or leakage connection ofthe injection valve (2), which adaptor head can be made to communicatewith a vacuum pump (16), and a device for supplying medium at highpressure to a standardly provided connection of the injection valve. 15.An apparatus for performing the method according to claim 11, theapparatus comprising: an adaptor head (14), to be connected to alow-pressure connection or leakage connection of the injection valve(2), which adaptor head can be made to communicate with a vacuum pump(16), and a device for supplying medium at high pressure to a standardlyprovided connection of the injection valve.
 16. An apparatus forperforming the method according to claim 12, the apparatus comprising:an adaptor head (14), to be connected to a low-pressure connection orleakage connection of the injection valve (2), which adaptor head can bemade to communicate with a vacuum pump (16), and a device for supplyingmedium at high pressure to a standardly provided connection of theinjection valve.
 17. An apparatus for performing the method according toclaim 13, the apparatus comprising: an adaptor head (14), to beconnected to a low-pressure connection or leakage connection of theinjection valve (2), which adaptor head can be made to communicate witha vacuum pump (16), and a device for supplying medium at high pressureto a standardly provided connection of the injection valve.
 18. Theapparatus according to claim 14, wherein the adaptor head (14) has aconnection that is in communication with a low-pressure connection for aflushing medium.
 19. The apparatus according to claim 14, wherein theapparatus further comprise a return tank (20) for the return quantity incommunication with the adaptor head (14).
 20. The apparatus according toclaim 18, wherein the apparatus further comprise a return tank (20) forthe return quantity in communication with the adaptor head (14).
 21. Theapparatus according to claim 14, further comprising at least oneswitching valve (V1, V2, V3, V4) for controlling chronological events ofthe apparatus.
 22. The apparatus according to claim 15, furthercomprising at least one switching valve (V1, V2, V3, V4) for controllingchronological events of the apparatus.
 23. The apparatus according toclaim 16, further comprising at least one switching valve (V1, V2, V3,V4) for controlling chronological events of the apparatus.
 24. Theapparatus according to claim 17, further comprising at least oneswitching valve (V1, V2, V3, V4) for controlling chronological events ofthe apparatus.
 25. The apparatus according to claim 21, furthercomprising a control device connected to a control terminal of the atleast one switching valve (V1, V2, V3, V4).
 26. The apparatus accordingto claim 22, further comprising a control device connected to a controlterminal of the at least one switching valve (V1, V2, V3, V4).
 27. Theapparatus according to claim 23, further comprising a control deviceconnected to a control terminal of the at least one switching valve (V1,V2, V3, V4).
 28. The apparatus according to claim 24, further comprisinga control device connected to a control terminal of the at least oneswitching valve (V1, V2, V3, V4).
 29. The apparatus according to claim25, wherein the control device is coupled to an electrical terminal ofthe injector.